It is known that HCPP or highly isotactic polypropylene, being polymer with a particularly low error rate, finds use in injection molding applications with usable handling characteristics and beneficial product results. Generally HCPP is recognized as a comparatively brittle material which is limited in its usefulness by its inherently brittle nature.
Use in film applications, particularly, has not been considered for HCPP in light of the material's tendency to be brittle, tear easily, and have an unpleasant or "hard" feeling to the touch.
Generally those in the field of development of useful polymer compositions have tended to bypass highly isotactic poly-.alpha.-olefin in light of its processing difficulty and properties liabilities. Such material is avoided in spite of the potential benefits to be gained from its high level of crystallinity including enhanced strength.
To take advantage of the properties of highly crystalline polyolefin yet mitigate its brittleness some have pursued composite or multi-layer films. An example of such strategy is found in JP 844 167 filed Dec. 1, 1984 and assigned to Sumitomo Chemical Industries, K.K.
Others, as demonstrated by Shel et al. in U.S. Pat. No. 5,603,696 as issued Feb. 18, 1997, have sought to gain advantage of moderate crystallinity of isotactic polypropylene by including up to about 15% of it in a blend of polypropylene with moderate syndiotactic character.
Goins et al. describe, in EP 747 430 published Nov. 12, 1996, blend of isotactic polypropylene and syndiotactic polypropylene having comparatively broad MWD, in an amount of up to 4 wt. %. Polymer used is, however, standard isotactic polypropylene, not the HCPP of the current invention.
Others, including DeLucia et al. describe, in WO 9623095, use the lower melt point or flow temperature of sPP simply to provide an agent for thermal point bonding in non-woven fabric applications. Use of HCPP in combinations with sPP, however, is not demonstrated.
JP 7 149 968 A, as published Jun. 13, 1995, JP 7 126 458 A as published May 16, 1995, and EP 650 818 A3 as published Jun. 14, 1995, all of which are assigned to Mitsui-Toatsu Chemical Company, describe resin of syndiotactic polypropylene and isotactic polypropylene, as well as their films.
A further example of attempts to gain some benefit from the crystalline nature of isotactic polypropylene but maintaining ease of processing is found in U.S. Pat. No. 5,603,696 in which minor amounts of isotactic polypropylene is included with a majority of sPP to form molded articles. This concept is applied again in U.S. Pat No. 5,269,807 in which suture material is produced from blended sPP and iPP or static PP.